The present invention relates to a hammer drill in general, and more particularly to a hammer drill having an improved construction.
Hammer drills per se are already known. One such prior-art construction has a rotary output shaft on which a disk member is mounted which during drilling use of the hammer drill is connected with projections formed on an impact member, which when the hammer drill is used purely for a drilling operation rotates with the output shaft. When the device is to be used for both drilling and impacting, that is when a hammering motion is superimposed upon the drilling operation, then switching-over from drilling operation results in an abrupt braking of the rotating impact member which now becomes blocked against rotation, whereupon rotating projections on the disk member cooperate with the now stationary projections of the impact member, alternately interdigitating with them and becoming disengaged from them, to impart to the output shaft a reciprocal movement by alternating movement of the impact member towards and away from the disk member.
However, it has been observed that the sudden blocking of the impact member against rotation can lead not only to undesired vibrations of the housing -- although during the subsequent actual hammer drill operation, the transmission of such vibrations to the housing and therefore to the user is largely avoided -- but can also lead to damage to components of the device, for instance cause damage to the bearings or the like. Evidently, this latter possibility is highly undesirable and although the transmission of vibrations to the housing and thereby to a user will normally occur only during the switching-over from drilling to hammer-drilling operation and not later when the hammer drilling operation is actually in progress, even this relatively brief period during which the transmission of vibrations occur, can be unpleasant for a user. Added to these disadvantages is the further drawback that this prior-art construction is relatively complicated and also comparatively bulky.